ci: use MAINTAINERS.json to check for core maintainers in thank you action

Signed-off-by: Shivansh Sahu <sahushivansh142@gmail.com>

Author: shivansh-gohem

MAINTAINERS.json

@@ -0,0 +1,10 @@
+{
+  "maintainers": [
+    "khanhtc1202",
+    "nghialv",
+    "ffjlabo",
+    "Warashi",
+    "t-kikuc",
+    "eeshaanSA"
+  ]
+}